Re: [PATCH v2] x86, vt-d: enable x2apic opt out

From: "Woodhouse, David" <david.woodhouse@intel.com>
To: "Song, Youquan" <youquan.song@intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"mingo@elte.hu" <mingo@elte.hu>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"hpa@linux.intel.com" <hpa@linux.intel.com>,
	"Kay, Allen M" <allen.m.kay@intel.com>,
	"Siddha, Suresh B" <suresh.b.siddha@intel.com>,
	"Liu, Kent" <kent.liu@intel.com>,
	Youquan Song <youquan.song@linux.intel.com>
Subject: Re: [PATCH v2] x86, vt-d: enable x2apic opt out
Date: Wed, 11 May 2011 18:21:13 +0100	[thread overview]
Message-ID: <1305134473.30435.178.camel@i7.infradead.org> (raw)
In-Reply-To: <1302764783-24491-1-git-send-email-youquan.song@intel.com>

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On Thu, 2011-04-14 at 08:06 +0100, Song, Youquan wrote:
> +               pr_info("Not enabling x2apic, firmware requests OS opt-out "
> +                         "x2apic.\n"); 

This output is far too innocuous. At the very least, it should have a
clear statement that this should leave you vulnerable to IRQ injection
attacks that intr-remapping + x2apic would have protected against.

It should probably look more like:

 WARN (1, "Your BIOS is broken and requested that x2apic be disabled\n"
    "This will leave your machine vulnerable to irq-injection attacks\n"
    "Use 'intel_iommu=no_x2apic_optout' to override BIOS request\n");

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation

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